1. Field of the Invention
This invention relates to a semiconductor pressure converter which uses a semiconductor, such as silicon, as a diaphragm for pressure detection and converts pressure into electrical signal by utilizing the semiconductor piezo-resistance effect; and, more particularly, to an improvement in the semiconductor pressure converter which is capable of adjusting various characteristics of the semiconductor pressure converter utilizing a shearing type gage without mutual interferences.
2. Discussion of the Prior Art
An existing circuit for obtaining an output voltage in response to pressure applied to semiconductor pressure detector comprises an ordinary type gage formed on the surface of a semiconductor diaphragm, wherein resistance value changes corresponding to applied pressure. The strain gage is formed in a bridge structure. A constant voltage is applied to a power supply end of the strain gage and an output voltage is obtained from an output end corresponding to the applied pressure.
Since the ordinary type gage is formed by a semiconductor material, the zero point changes depending on slight differences of temperature of each ordinary type gage forming the bridge circuit.
It is known to connect resistance material having a resistance temperature coefficient which is different from the resistance temperature coefficient of the ordinary type gage in series or parallel to the ordinary type gage to compensate for temperature point shift.
Some ordinary type gages do not change in a linear manner the resistance change for increase of applied pressure and tend to show reduction of sensitivity of resistance change in accordance with increase of pressured applied. In this case, an output signal of a bridge circuit for applied pressure is detected by a first amplifier and is then fed back in positive to a second amplifier which supplies a voltage to the power supply end of the bridge circuit. In this manner, a voltage applied to the bridge is boosted with increase of applied pressure and reduction of sensitivity can be prevented. Moreover, relation of output voltage to applied pressure is linearized.
However, the circuit which compensates for temperature zero point shift, as explained previously, further requires a resistance for zero adjustment of unbalance of the bridge circuit which is generated when the resistance material for compensation is connected in series or parallel to the ordinary type gage. These resistances generate temperature variations if these are not equivalent to the temperature coefficient of the gages. In addition, since the temperature coefficients of different gages are different, it is difficult to adjust the temperature coefficient. Moreover, series and parallel connections of resistances to gages result in the disadvantage that span is influenced and adjustment is complicated.
Moreover, the existing linear compensation circuit, wherein an output voltage of the first amplifier is additionally applied to the second amplifier for addition to the power supply of the bridge circuit still has the following deficiencies. If the first amplifier contains an offset voltage, for example, the voltage including this value is fed back and the characteristic of the second amplifier effects direct influence on the amount of compensation for linearization. For example, the amount of feedback itself changes when the degree of amplification of the first amplifier changes. Adjustment of linearity requires complicated procedures in case the amplifier is given zero adjustment, span adjustment and temperature compensation function, which are usually required. As described above, if the respective adjustments are improperly done, repeated adjustments may be required by changing many times the ambient temperature during temperature compensation. Accordingly, adjustments become expensive.
Thus, the prior art arrangements still leave something to be desired.